Quick question about appraisal rules when comping

[Korey Harmon]

I'm trying to practice running comps on properties online and get used to appraisal rules. The thing I'm confused about is when it comes to subtracting/adding for carports, pools, and garages. For example, if neither property has a garage, do I just not subtract or add at all? Sorry if it's a stupid question, I just want to be sure.